Electrostatic dust precipitators and ion generators are conventionally operated with rubber insulated cables, crosslinked polyethylene insulated cables, or polyethylene insulated cables. Crosslinked polyethylene insulated cables and polyethylene insulated cables have good electrical characteristics and are easy to service and handle. However, these cables are not completely satisfactory in terms of flexibility and long-term stability and, particularly, sometimes insulation breakdowns within a relatively short period of time if they are exposed to peculiar conditions in field use, for example, in the case of where the cable is used for an electrostatic dust precipitator or an ion generator in which the cables suffer from cyclic application of voltage with damped ocillation. It has therefore been desired to develop an insulated electrical cable that is highly flexible and exhibits superior long-term stability.